1. Field of the Invention
The present invention relates to a crystalline synthetic resin composition, in particular, a crystalline synthetic resin composition comprising a synthetic resin compounded with an alkali metal compound and a basic polyvalent metal salt of a cyclic organophosphoric ester and having improved transparency, mechanical properties, etc.
1. Description of the Prior Art
Crystalline synthetic resins such as polyethylene, polypropylene, polybutene-1, polyethylene terephthalate, polybutylene terephthalate, polyphenylene sulfide and polyamide suffer from the fact that their mold cycling efficiency is low due to a low crystallization rate after heat melt molding and that they shrink due to the crystallization which proceeds after the heat molding. Other defects of these crystalline synthetic resins include an insufficient strength and a poor transparency due to the formation of large crystals.
It is known that all of these defects are due to the crystallinity of the synthetic resins and that the defects can be overcome by elevating the crystallization temperature of the synthetic resins so that fine crystals can be rapidly formed.
It is known to add a nucleating agent or a crystallization accelerator in order to overcome these defects, and those used heretofore include metal salts of carboxylic acids, such as aluminum 4-tert-butylbenzoate and sodium adipate; metal salts of acidic phosphoric esters, such as sodium bis(4-tert-butylphenyl) phosphate and sodium 2,2'-methylenebis(4,6-di-tert-butylphenyl) phosphate; and polyhydric alcohol derivatives such as dibenzylidenesorbitol and bis(4-methylbenzylidene)-sorbitol.
Among these compounds, metal salts of cyclic phosphoric esters of alkylidenebisphenols described in, for example, Japanese Patent Laid-Open Nos. 1736/1983 and 184252/1984 have remarkable effects and, therefore, they are widely used.
It has also been attempted to improve the effects of these compounds by combining them with other metal compounds. For example, Japanese Patent Laid-Open No. 69853/1988 discloses a method of preventing the rigidity from being reduced when an alkali metal aromatic phosphate nucleating agent is used in combination with an alkaline earth metal carboxylate such as calcium stearate by using hydrotalcite or an alkali metal carboxylate in place of the alkaline earth metal carboxylate; Japanese Patent Laid-Open Nos. 129050/1989 and 129051/1989 disclose a method wherein a combination of a metal salt of a cyclic organophosphoric ester with a salt of an aliphatic carboxylic acid with a group II metal of the periodic table is used; Japanese Patent Laid-Open Nos. 79649/ 1991 and 81368/1991 disclose a method wherein a combination of an acidic organophosphoric ester compound with a metal salt of an aliphatic carboxylic acid is used; and Japanese Patent Laid-Open No. 43437/1991 discloses a method of preventing the pH from lowering by immersion of a metal salt of a cyclic organophosphoric ester in hot water after irradiation with a radiation by combining it with a hydroxide of an alkali metal, alkaline earth metal or aluminum-group metal.
However, the effects obtained even by the abovedescribed combinations are yet unsatisfactory in practice, and a further improvement has been demanded particularly in the transparency of the crystalline synthetic resins.
Although Japanese Patent Laid-Open Nos. 104638/ 1989, 104639/1989 and 104647/1989 disclose the use of a basic aluminum salt of an aromatic phosphoric diester in order to improve the processability and thermal rigidity of a high-rigidity propylene resin, scarcely any effect of improving the transparency is obtained by using such a compound. It has been supposed that such a basic polyvalent metal salt compound has only a poor effect of improving the transparency of the crystalline synthetic resins.